1. Field of the Invention
The present invention relates generally to endoluminal tubular prostheses, such as stents, stent-grafts, and other structures. More particularly, the present invention provides modular tubular prosthesis structures having properties which can be tailored for individual body lumens, including blood vessels, particularly for the treatment of abdominal and other aneurysms.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending distally into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper sizing of endovascular prostheses can be problematic.
Proper matching of the prosthesis to the blood vessel is critical to the treatment of an aneurysm. The prosthesis preferably extends axially beyond the weakened portion of the blood vessel to anchor securely in the healthy vessel wall. However, the cross-sectional size and axial length of individual blood vessels vary considerably between patients. Even within a patient, the cross-section and resilience of a lumen wall can vary considerably along its axial length, and the location and extent of the aneurysm will differ with different patients. Additionally, each prosthesis must be carefully constructed and handled, making it extremely costly to provide and maintain the large selection of prostheses required for proper fitting of every individual patient.
Known intraluminal prostheses may generally be characterized as either resilient, locking, or malleable structures. Resilient intraluminal prostheses are often formed as stent-grafts which radially conform to adapt to variations in lumen cross-section, and which will also accept some axial curvature. However, the stent-graft structures themselves have typically been formed with simplistic cylindrical frames or "stents" having axially constant diameters, constant expansive forces, and constant flexibilities along their lengths. A separate cylindrical liner or "graft" is typically attached to the frame to prevent blood flow through a ruptured vessel wall. Such liners are typically inelastic to prevent pressure from distending a weakened luminal wall. Unfortunately, inelastic liners can wrinkle or fold when the stent-graft is radially compressed from a fully expanded size, or when a portion of the liner is axially compressed by, for example, axially bending of the prosthesis. Such wrinkles or folds in the liner can substantially occlude the flow through the lumen of the prosthesis, or may result in leakage around the perimeter of the prosthesis.
Additionally, resilient stent-grafts must expand against the luminal wall with sufficient force to anchor the prosthesis within the body lumen, and should ideally be sealed around the perimeter of the luminal wall to prevent leakage. A cylindrical stent-graft large enough to provide such an anchor and seal against a healthy luminal wall may, in some patients, also impose an unacceptably high resilient expansive force at the aneurysm or other disease condition. Therefore, effective endoluminal prosthetic therapies require accurate fitting, even of resilient prosthesis, to the specific disease site and to the individual patient's vascular system.
On the other hand, malleable intraluminal prostheses can usually be expanded to fit the lumen when implanted, but the expanded prosthesis generally does not conform to irregular luminal cross-sections. The expanded prosthesis must be sufficiently rigid and sufficiently large to provide a stable anchor. Malleable prostheses are therefore expanded mechanically in situ, typically with a balloon catheter. The problem is that the expanded prosthesis assumes the shape of the cylindrical balloon catheter rather than the irregular shape of the body lumen. Furthermore, the entire perimeter of the prosthesis must be in contact with the luminal wall to provide sealing. Hence, the luminal wall is forced to assume a circular cross-section and is generally distended to a relatively large diameter.
For these reasons, it would be desirable to provide improved endoluminal prostheses, including stents and stent-grafts, and improved methods for placement of such endoluminal prostheses to treat aneurysms and other conditions. It would further be desirable to provide endoluminal prostheses which accept variations in geometry along body lumens without compromising their therapeutic effectiveness. It would further be desirable to provide adaptable prostheses and methods for their placement which would facilitate effective treatment of widely varying luminal system geometries without requiring an excessive inventory of prostheses to chose from.
2. Description of the Background Art
U.S. Pat. No. 5,064,435 describes a self expanding prosthesis which maintains a stable axial length during expansion by anchoring of radially outward flares at each end, and by sliding of an overlapping medial region therebetween.
Vascular grafts and devices for their endoluminal placement are described in U.S. Pat. Nos. 5,282,824; 5,272,971; 5,242,399; 5,219,355; 5,211,658; 5,201,757; 5,192,297; 5,190,058; 5,158,548; 5,147,370; 5,104,399; 5,092,877; 5,078,726; 5,019,085; 4,990,151; 4,950,227; 4,913,141; 4,886,062; 4,820,298; 4,787,899; 4,617,932; 4,562,596; 4,577,631; and 4,140,126; and European Patent Publications 539,237; 533,511; 518,839; 518,704; 508 473; 505,686; 466 518; and 461 791. Catheters for placing vascular stents are described in U.S. Pat. Nos. 5,192,297; 5,092,877; 5,089,005; 5,037,427; 4,969,890; and 4,886,062. Catheters carding a graft structure in a tube or capsule are described in U.S. Pat. Nos. 5,275,622; 5,104,399; and 4,787,899; and EP466518.